A conversion system is known from the document U.S. Pat. No. 6,169,677. The object of such a conversion system is to make it possible to connect in parallel a plurality N of identical polyphase voltage inverters, with interleaving of the pulses, in such a way as to improve the waveform of the output voltage, putting in parallel the N inverters making it possible to obtain an output voltage of a higher power. FIG. 1 shows such a conversion system.
It is specified that two points marked by the same letter in FIG. 1 and in the other figures described below are, by convention, connected to each other by an electrical link, which is not shown to make the diagram easier to read.
FIG. 1 shows three three-phase inverters 2A, 2B, 2C, which are connected in parallel with a single bus 4 for circulation of an electrical input direct current. The input bus 4 includes a capacitive mid-point 5, which is connected to electrical earth. Each inverter 2A, 2B, 2C is suitable for converting the input direct current into an intermediate three-phase current, which is supplied to three intermediate terminals Ui, Vi, Wi, where i equals 1, 2 or 3 respectively, corresponding respectively to the inverters 2A, 2B, 2C. Each intermediate terminal Ui, Vi, Wi corresponds to a respective phase of the intermediate three-phase current. The conversion system also comprises three magnetic couplers 6A, 6B, 6C, each being arranged at the output of a respective inverter 2A, 2B, 2C. Each of the three magnetic couplers 6A, 6B, 6C comprises three electromagnetic coupling coils 8, all identical. Each coupling coil 8 is wound around a respective core 10, the three cores 10 of a magnetic coupler 6A, 6B, 6C being connected to each other by magnetic linking bars 12. A core 10 which is equipped with a coupling coil 8 forms a coiled column.
The three coupling coils 8 of the first magnetic coupler 6A are each connected by one of their ends to a respective intermediate terminal U1, U2, U3, the intermediate terminals U1, U2, U3 corresponding to the first phase of each three-phase inverter 2A, 2B, 2C, and by their other end to a single output terminal U, corresponding to the first phase of the three-phase output current.
Similarly, the three coupling coils 8 of the second magnetic coupler 6B are each connected by one of their ends to a respective intermediate terminal V1, V2, V3, and by their other end to a single output terminal V, corresponding to the second phase of the three-phase output current. Similarly, the three coupling coils 8 of the third magnetic coupler 6C are each connected by one of their ends to a respective intermediate terminal W1, W2, W3, and by their other end to a single output terminal W, corresponding to the third phase of the three-phase output current.
In conversion systems of this type (FIG. 1 Prior Art), the number of coiled columns of each magnetic coupler 6A, 6B, 6C equals the number of inverters 2A, 2B, 2C in parallel.
However, conversion systems of this type are not modular, since adding an inverter, in parallel with the other inverters which are already present, makes it necessary to add a magnetic core equipped with a coupling coil in each magnetic coupler. Also, conversion systems of this type generate relatively large line voltage drops.